Electronic control circuit

ABSTRACT

An electronic control circuit for use with a heater, a fan, a humidifier or any device utilizing a power mode switch and a condition sensor, the electronic control circuit including a single control switch for controlling both power output and responding to a sensed condition. The electronic circuit includes a microprocessor, preferably in the form of an application-specific integrated circuit to provide the circuit logic. The single control switch is preferably a push-button switch which places the unit in the selected mode of operation. The electronic control circuit also includes a thermistor or humidity sensor to sense conditions and, depending upon the set temperature/humidity by the control switch and the sensed condition the unit will operate accordingly. The unit can also operate in a manual mode, thereby bypassing the sensor operation.

PRIORITY APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.60/200,586, filed on Apr. 28, 2000.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an improved electronic control circuit,and more particularly, to an electronic control circuit which providesthe functions of a multi-position power switch and a sensor device tocontrol operation of an apparatus.

2. Description of Prior Art

Presently available electric space heaters and electric fans fordomestic use are generally provided with at least two controlcomponents. The first control component is a multi-position power switchto select a proper setting, e.g. off/high/medium/low. The second controlcomponent is a thermostat to de-energize the device when apredetermined, pre-set temperature value is achieved. Likewise currentlyavailable humidifiers are provided with a similar multi-position powerswitch and, rather than a thermostat, are provided with a humidistat tosense when a predetermined, pre-set humidity level is achieved.

The present multi-position power switches and mechanicalthermostats/humidistats are expensive, unreliable, and mechanicallycomplex. Additionally, these components constitute as a major portion ofthe cost and complexity in making and using low cost heaters, fans andhumidifiers. Furthermore, the mechanics of these components tend torender them the most oft failed components in the device. Morespecifically, each component requires a control knob and individualwiring connections, which are labor intensive and points of potentialfailure.

OBJECTS AND SUMMARY OF THE INVENTION

It is an object of the present invention to provide an electroniccontrol device in a heater, a fan or a humidifier which eliminates theuse of complex switches and reduces wiring connections to improvereliability.

It is yet a further object of the present invention to provide anelectronic control device in a heater, a fan or a humidifier which issimple to construct thereby reducing complexity of construction andlowering the cost of same.

It is yet a further object of the present invention to provide anelectronic control device in a heater, a fan or a humidifier whichimproves the reliability of the operation.

It is still another object of the present invention to provide a solidstate electronic control device which uses a single actuator to set adesired operating level (high, medium, or low) as well as apredetermined temperature/humidity value at which power to the unit isto be terminated.

It is another object of the present invention to provide an electroniccontrol circuit for use in a heater, a fan or a humidifier which uses asingle push button to both turn the unit on, set an operating powerlevel and set a predetermined threshold temperature/humidity value toachieve by operation of the unit.

In accordance with one form of the present invention, an electroniccontrol circuit is provided for operating a device such as a heater, afan, a humidifier or any other device which includes an operating powerlevel and a pre-set value for comparison with a sensor device. Theelectronic control circuit includes a single control switch for turningon the device and selecting a mode of operation. The mode of operationincludes both a power level of operation and one of a plurality ofpre-set values. The sensor is provided for sensing a condition. Theelectronic control circuit further includes a comparator for comparingthe sensed condition to the selected pre-set value. The electroniccontrol circuit includes a means for providing operating power to thedevice in response to an output from the comparator. In a preferredembodiment, the single control switch is a push-button switch.Furthermore, the means for providing operating power to the deviceincludes an application-specific integrated circuit.

In one embodiment, the electronic control circuit is used in anapparatus for modifying ambient air conditions. The apparatus includes ahousing, a fan assembly positioned within the housing and including amotor and a fan blade attached to the shaft of the motor. The apparatusfurther includes an electronic control circuit electrically coupled tothe motor and adapted to provide power thereto. The electronic controlcircuit has a single switch to turn on operating power to the apparatusand to select a pre-set threshold ambient air condition. The electroniccontrol circuit further includes a sensor for sensing an ambient aircondition and a means for comparing the pre-set threshold ambient aircondition to the sensed ambient air condition. The electronic controlcircuit provides power to the fan assembly motor to substantiallyachieve the pre-set threshold ambient air condition in view of an outputof the comparing means and terminates power to the fan assembly motorwhen the pre-set threshold ambient air condition is substantiallyattained. Preferably, the switch is a push-button switch and theelectronic control circuit includes a plurality of discretelyincremented pre-set threshold ambient air condition values which can beselected by repeatedly activating the switch. The apparatus furtherincludes indicia, such as light emitting diodes, to indicate both thepower level of operation and the selected pre-set threshold ambient aircondition.

The logic for the electronic control circuit is provided by anapplication-specific integrated circuit to control power to theapparatus motor and to illuminate the indicia associated with the modeof operation. The sensor may comprise a thermistor in the case of a fan,a heater, a griddle, or the like or a humidity sensor for use with ahumidifier. With respect to humidifiers, the electronic control circuitcan be used with either a cool mist humidifier which utilizes a fan anda wick filter immersed in a pool of water or with a warm mist humidifierwhich includes a heating element for creating steam to be released tothe surroundings.

The present invention is also directed to a method of operating anapparatus for modifying an ambient air condition. The apparatus includeseither a heating element or a fan assembly wherein the fan assemblyincludes a motor and a fan blade coupled to the shaft of the motor. Theelectronic control circuit is electrically coupled to either the heatingelement or the fan motor, or both, for providing operating powerthereto. The electronic control circuit includes a single control switchand a sensor for sensing an ambient condition. The apparatus is operatedby actuating the single control switch to turn on the apparatus and toselect an operating power level and a pre-set threshold ambient aircondition value. The pre-set threshold ambient air condition is comparedto the sensed ambient air condition and operating power is provided tothe heating element, the motor or both if the sensed ambient aircondition is not substantially similar to the pre-set ambient aircondition. Power is terminated to the device when the sensed ambient aircondition is substantially similar to the pre-set threshold ambient aircondition. The method further includes repeatedly actuating the switchto progress through a plurality of operating modes and pre-set thresholdambient air condition values.

A preferred form of the electronic control circuit, as well as otherembodiments, objects and advantages of this invention, will be apparentfrom the following detailed description of the illustrative embodimentsthereof, which is to be read in connection with the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a heater including a first embodiment ofthe electronic control device of the present invention.

FIG. 2 is a cross-sectional view of the heater illustrated in FIG. 1.

FIG. 3 is an electrical schematic of the electronic control circuit forthe heater illustrated in FIGS. 1 and 2.

FIG. 4 is an electrical schematic of the electronic control circuit foruse with a box fan.

FIG. 5 is an electrical schematic of the electronic control circuit foruse with a window fan.

FIG. 6 is an alternative embodiment of the heater formed in accordancewith the present invention.

FIG. 7 is an electrical schematic of the electronic control circuit forthe heater illustrated in FIG. 6.

FIG. 8 is an electrical schematic of the electronic control circuit ofthe present invention utilizing a standard microcontroller.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIG. 1, a heater is shown utilizing a first embodiment ofthe electronic control device of the present invention. Although, FIG. 1illustrates a heater, it is envisioned that the electronic controlcircuit of the present invention is equally adaptable to be used in afan including a thermostat or a humidifier including a humidistat. Forexample, the same device illustrated in FIG. 1 may be operated as a fanwith a thermostat by removing the heating element from the unit. Atypical structure for a window fan including a thermostat is disclosedin commonly owned U.S. Pat. No. 5,660,605 entitled “Window Fan”, thedisclosure of which is incorporated herein by reference. Likewise, acool mist humidifier may be operated which uses a wick filter and a fanto draw air through the filter to add moisture to the surroundings usinga similar electronic control circuit. The structure of a cool misthumidifier is disclosed in commonly owned U.S. Pat. No. 5,529,726entitled “Evaporative Humidifier”, the disclosure of which isincorporated herein by reference. Similarly, the electronic controlcircuit can be employed in a warm mist humidifier having a humiditysensor. A typical structure for a warm mist humidifier is disclosed incommonly owned U.S. Pat. No. 5,792,390 entitled “Humidifier with TopFill Tank”, the disclosure of which is incorporated herein by reference.It is contemplated that the single-button electronic control circuitdisclosed herein is also capable of operating any type of unit whichrequires both power level control and achieving a set temperature, suchas an electric cooking device. For example, the electronic controlcircuit of the present invention is useful in controlling an electricgriddle which includes a heating element and a set temperature value.

In the embodiment of FIG. 1, the electronic control circuit includes asingle switch, namely a push-button switch having a manual and automaticmode of operation. It is also envisioned that other types of switchescan be used, however, a push-button switch allows for easy operation andis low in cost. More specifically, in the manual mode, the device, e.g.a heater, a fan or a humidifier, can be operated at either high, medium,or low power regardless of the ambient temperature or humidity level.Alternatively, the device may be operated in an automatic mode basedupon a sensed temperature/humidity and a predetermined thresholdtemperature or humidity set point or value set by the user. For example,in the case of a heater, the automatic mode may include a temperatureset point of 70° F. If the unit is set in automatic mode to 70° F., theheater will operate at a selected power level, until ambient temperaturesensed by a thermostat reaches 70° F. Once the set point temperature isattained, the electronic control device of the present inventionde-energizes the unit until the sensed temperature once again fallsbelow the set point temperature and the unit is once again turned on. Asnoted earlier, the same type of electronic control circuit is equallyapplicable to a fan equipped with a thermostat or a humidifier equippedwith a humidistat.

Referring again to FIG. 1, the heater 10 includes a push-button switch12 to operate the electronic control circuit. A series of light-emittingdiodes (LED's) 14 are provided around the periphery of the push-buttonswitch 12 to provide a visual indication as to the mode and setting ofoperation of the unit. The single push-button switch and associatedcircuitry replaces the functions of previously used multi-positionswitches and thermostats/humidistats.

FIG. 2 is a front cross-sectional view of FIG. 1 illustrating thecomponents of the heater 10. The heater includes a heater housing 15 forsupporting therein a fan assembly comprising a motor 16 and a fan blade18. The motor 16 includes a shaft (not shown) which is mechanicallyconnected to the center hub of the fan blade to rotate the bladeproducing air flow which exists the front grille. It is envisioned thatthe fan assembly may take any known form so long as air is drawn acrossthe heating element for discharge to the surroundings. The heater 10also includes a heating element 20 to produce the heated air to bedischarged from the unit. In this illustration, the heating element isin the form of a circular element, however, many different types ofheating elements may be used as is well known by those of ordinaryskill.

The heater 10 uses an electronic control circuit to operate the heatingelement and fan. As illustrated in FIG. 2, the electronic controlcircuit is preferably in the form of a printed circuit board 22 having alogic circuit in the form of an application-specific integrated circuit(ASIC) 24 programmed to perform the specific logic of the electroniccontrol circuit to operate the heater. The ASIC 24 is electronicallycoupled to both the heating element and fan motor via printed traces onthe circuit board as well as wires, 26 and 28, respectively. Theelectronic control circuit also includes a thermostat 30 coupled to theASIC 24 via wires coupled to the printed circuit board 22. Thethermostat 30 senses ambient air temperature and provides theinformation to the microprocessor for comparison to the predeterminedthreshold temperature set by the user via the push-button switch.

FIG. 3 illustrates the electronic control circuit for use with a heater.The ASIC U1 is a collection of logic circuits having the specific logicrequired for operation provided therein. A suitable ASIC is produced byThe Holmes Group, Inc., a Massachusetts Corporation under Part No.“Holmes Accutemp ASIC”.

Furthermore, the ASIC includes a comparator for comparing the sensedambient temperature/humidity value to the pre-set value selected by theuser. The electronic control device circuit also includes a triactrigger circuit to provide power to the unit being operated. Contrary toa microprocessor which can be programmed to perform a variety offunctions, the ASIC is designed to perform the specific functions forwhich it is programmed. Accordingly, ASIC's are typically lower in unitcosts and provide higher performance by eliminating the circuit from thechip needed to make it programmable and incorporating just those logicfunctions needed for the application. The higher performance comes fromdirectly implementing the logic instead of using an instruction setrequiring multiple clock pulses to execute.

As illustrated in FIG. 3, the heater uses a single push-button controlswitch S1 to control operation of the unit and seven (7) LED's toindicate the mode of operation. Naturally, other types of controlswitches and varying numbers of LED's may be used depending upon thenumber of modes and settings chosen by the designer. The ASICmicroprocessor U1 uses the input A/C power from a standard 120 volt, 60Hz outlet to perform timing functions and to determine when to fire atriac Q1 that controls operation of the heating element and fanassembly. The input power is provided to the electronic control circuitvia pads J2 and J3 on the printed circuit board. The hot A/C input ispassed through a power supply rectifier which includes components D1 andR5 arranged as shown in FIG. 3. It should be noted that diode D1 isarranged to provide negative voltages to the ASIC U1 at pin 9 labeledVSS. Resistor R5 provides current regulation and resistor R4 provides asample of the AC line frequency to determine when to fire the triac andfor internal timing function. The A/C neutral is provided to the pin 1,VCC, of the ASIC U1. Negative going pulses on pin 15 labeled TRIAC ofthe ASIC UI fire the triac Q1. The A/C neutral is also provided to thetriac Q1. Capacitor C1 protects the ASIC from transients on the A/Cpower line. Capacitor C2 acts as a filter capacitor for the power supplyto reduce ripple thereon.

The ASIC U1 further includes an internal oscillator, whose frequency isdetermined by an external RC network, R2 and C5 coupled to pin 11. TheRC network is used to generate a higher frequency for operations thatrequire smaller time increments than can be obtained from the input 60Hz line through pin 16 labeled CLOCK. The electronic control circuit hasbeen engineered to draw a relatively constant current, regardless of themode of operation. Therefore, no voltage regulation is required.Furthermore, by changing the value of resistor R2, the frequency of theinternal oscillator can be changed thereby delaying the firing of thetriac in the low power mode of operation. Thus, the ASIC U1 can be usedin a wider range of applications.

The electronic control circuit further includes a thermistor T1 coupledto the ASIC microprocessor U1 via printed circuit board pads J4 and J5.Capacitors C6 and C7 along with thermistor T1, set the frequency of anoscillator inside the ASIC. As the temperature changes the value ofthermistor T1, the oscillator frequency changes thus enabling the ASICto measure temperature.

The ASIC U1 also includes outputs to each of the LED indicators whichprovide visual indicia as to the mode of operation of the heater. TwoLED's provide indication of the power level, either high (D2) or low(D3) and the remaining LED's provide indication as to the predeterminedthreshold temperature at which the heater will be turned on, i.e., 65°F. through 80° F. in 5° increments, D4-D8, respectively.

As discussed earlier, the ASIC and associated electronic control circuitcan be used to operate either a heater, a fan or a humidifier. Toaccomplish this function, the ASIC U1 includes a programming pin thatcan be tied to either the DC power voltage or ground thereby identifyingwhatever the ASIC is operating, a heater or a fan. A similar circuit maybe used in a cool mist humidifier by exchanging the thermistor with ahumidity sensor.

The ASIC logic also permits the heater to be operated in a manual mode,i.e. constant operation at a selected power level or in an“automatic”mode using the input from the thermistor to determine if theset threshold temperature has been reached and only operate the heaterand fan by firing the triac when the temperature is below or above theset temperature, respectively.

Operation of the heater using the push-button switch S1 requires aseries of pushes of the switch to proceed through the sequence ofoptions available. When power is first applied to the electronic controlcircuit by plugging the unit into the wall outlet, an internal power onreset circuit in the ASIC turns off all external signals. The first pushof the control button or switch places the heater in manual high powermode lighting the high LED and causing a pulse to fire the triac nearthe zero crossing of the A/C power. In case of a large fan which has alarger fan motor providing an inductive load, a second pulse is alsogenerated approximately 2.2 m sec. after the zero crossing so that thetriac can be turned on when enough holding current is present to keep iton.

A second push of the control button places the heater in the manualoperation low power level mode thereby lighting the low LED. The triacis fired with a delay sent by the frequency of the RC oscillator asdetermined by the values of resistor R2 and capacitor C5 to place theunit in the low power mode of operation.

A third push on the control button places the heater in the “automatic”mode at high power. Specifically, the “automatic” mode is defined asoperating to a predetermined set point and comparing the set temperaturewith the sensed ambient temperature of the thermistor. This third pushlights both the high LED and 80° F. LED and sets a thermostattemperature of 80° F. In this mode, when operating as a heatercontroller, the triac fires when sensed ambient temperature is below 79°F. thereby supplying power to the heating element and fan motor. Thetriac does not fire when the ambient temperature is above 81° F. and theheater remains off until the temperature drops below 79° F. If theelectronic control circuit were controlling a fan, the triac would beturned on when the sensed ambient temperature rises above the settemperature and turns off when sensed ambient temperature drops belowthe set temperature. The off and on limits are one degree above andbelow the set temperature to prevent the unit from cycling on and offrepeatedly.

Subsequent pushes of the control button changes the temperature settingin five degree increments as follows: 75° F., 70° F., 65° F., and 60° F.Following the high power level, 60° F. setting, the next push causes theheater to go into the low power level mode and the 80° F. temperaturesetting. Accordingly, in this setting, the heater operates at low powerto achieve and maintain a sensed ambient temperature of 80° F. Thus, thelow LED is lit as well as the 80° F. LED. Subsequent pushes of thecontrol button moves the set temperature through the set increments atlow power levels until the low power, 60° F. mode is reached. The nextpush on the control button places the electronic control circuit and theASIC in the “off” mode and turns off all LED's and stops firing thetriac.

As a matter of convenience, at any time during the setting sequence, ifthe push button is held down for more than one (1) second in any mode ofoperation, the electronic control circuit enters the “off” mode. Whenthe control button is pushed again, the electronic control button ispushed again, the electronic control circuit and ASIC returns to themode setting it was in prior to being turned off by the prolonged pushof more than (1) second.

Furthermore, as discussed above, the electronic control circuit ASIClogic provides for a range of temperature around the set pointtemperature in which the operation of the unit begins and is terminated.More specifically, in the case of a heater, the sensed ambienttemperature must be at least one degree above the set temperature beforethe unit will shut off. Likewise, the temperature must be at least onedegree below the set temperature for the unit to turn on. Otherwise, theunit would turn on and off excessively around the set temperature.

FIG. 4 is an electrical schematic of an electronic control circuit ofthe present invention for use with a box fan. Like components from theschematic of FIG. 3 have the same reference designations. However, thevalues for some of the components have been adjusted to be more suitablefor use with the inductive load of a fan. For example, capacitor C7 isno longer needed and an RC network including resistor R1 and capacitorC3 has been added in parallel to the firing triac to compensate for theinductive load of the fan. With respect to operation of the box fan, anidentical sequence of activations of the push button switch, i.e.control button, yields identical modes of operation. It should also benoted that pin 10 of the ASIC is no longer tied to pin 9 and groundthereby operating the ASIC in the “fan” mode rather than the “heater”mode.

FIG. 5 is an electrical schematic of an electronic control circuit ofthe present invention for use with a window fan. Once again, likecomponents of different values from FIGS. 3 and 4 have the samereference designation. Since the window fan motor is not a largeinductive load, there is no need for the RC network in parallel with thefiring triac used in connection with box fan application of the circuit.

FIG. 6 is an alternative embodiment of a heater using the single controlswitch and electronic control circuit as illustrated in FIG. 7. In thisembodiment, the heater has three power level settings, high, medium andlow and an additional temperature setting of 55° F. It is contemplatedas part of the present invention to have any given number of power levelsettings as well as any given number of temperature/humidity settings.

The heater illustrated in FIG. 6 having the electronic control circuitshown in FIG. 7 operates by repeated pushing of the push-button throughthe following sequence of operating conditions:

Originally in “off” position;

First push, provides continuous operation and a high power settingregardless of temperature with the corresponding high LED illuminating;

Second push provides continuous operation at medium power settingregardless of temperature with the corresponding medium LEDilluminating;

Third push provides, continuous operation on low power settingregardless of temperature with the corresponding low LED illuminating;

Fourth push provides operation at a predetermined power level whenambient temperature is less than 55° F.; if sensed ambient temperatureis greater than 55° F., power to the heating element and fan isterminated until sensed ambient temperature falls below 55° F.Subsequent pushes moves the sequence through the incremented temperaturesettings until the 80° F. mode is reached. The next push turns unit off.

As illustrated in FIG. 6, the LED's are individually labeled accordingto each of the above-identified operating conditions. Only theappropriate LED is illuminated at any given time.

Although the electronic control circuit may be constructed of discretelogic components, in order to be cost effective and most reliable, theelectronic control circuit of the present invention is preferably in theform of a printed circuit board including a microcontroller and morepreferably in the form of an ASIC having the driving software customizedthereon.

FIG. 7 is an electrical schematic of the electronic control circuit ofan alternative embodiment utilizing an ASIC to achieve the desiredfunctions. In the electrical schematic of FIG. 7, it is assumed that theASIC includes an analog to digital converter and an internal oscillator.The circuit also uses a voltage regulator D1.

FIG. 8 illustrates a similar electronic control circuit schematic tothat of FIG. 7, except that the circuit utilizes a commonly availablemicroprocessor rather than an ASIC. The circuit of FIG. 8 also includesa thermostat/humidistat sensor for sensing ambient temperature/humidityand a triac trigger circuit to provide power to the unit being operated.

As discussed above, the circuit of FIG. 8 is somewhat more complicatedincluding additional electrical components to achieve the same resultsas the circuit using the ASIC. However, the operation of the circuitwould be similar to that described above with respect to the heatercircuits shown in FIGS. 3 and 7.

The electrical components and values illustrated in FIGS. 3, 4, 5, 7 and8 are provided for illustrative purposes only. It is contemplated thatother components arranged in a different manner can accomplish thefunctions attained in the present invention and fall within the scopethereof.

What is claimed is:
 1. An apparatus for modifying ambient air conditionscomprising: a housing, a fan assembly positioned within the housing andincluding a motor and a fan blade attached to a shaft of the motor; andan electronic control circuit electrically coupled to the motor, andadapted to provide power thereto, the electronic control circuitcomprising a single switch to turn on operating power to the apparatusand to set a mode of operation to one of manual mode and automatic mode,wherein the single switch sets a plurality of pre-determined powerlevels of operation in manual mode, and further wherein the singleswitch selects a pre-set threshold ambient air condition in automaticmode, the electronic control circuit further including a sensor forsensing an ambient air condition and a means for comparing the pre-setthreshold ambient air condition to the sensed ambient air condition,wherein the electronic control circuit provides power to the fanassembly motor to substantially achieve the pre-set threshold ambientair condition and terminates power to the fan assembly motor when thepre-set threshold ambient air condition is substantially attained whenset in automatic mode.
 2. The apparatus as defined in claim 1, whereinthe switch is a push-button switch.
 3. The apparatus as defined in claim1, wherein the electronic control circuit includes a plurality ofdiscretely incremented pre-set threshold ambient air condition values.4. The apparatus as defined in claim 3, wherein each pre-set thresholdambient air condition value includes indicia associated therewith. 5.The apparatus as defined in claim 4, wherein the indicia comprises lightemitting diodes.
 6. The apparatus as defined in claim 1, wherein thepredetermined power level of operation includes at least low and high.7. The apparatus as defined in claim 1, wherein the electronic controlcircuit includes an application-specific integrated circuit to controlpower to the fan assembly motor and illuminate indicia associated with amode of operation for said apparatus.
 8. The apparatus as defined inclaim 1, wherein the comparing means comprises a comparator circuit. 9.The apparatus as defined in claim 1, wherein the sensor comprises athermistor and said apparatus is a fan.
 10. The apparatus as defined inclaim 1, further comprising a heating element electrically coupled tothe electronic control circuit and wherein the sensor is a thermistorand the electronic control circuit controls operating power to theheating element and motor.
 11. The apparatus as defined in claim 1,further comprising a wick filter element, wherein said housing includesa means for holding water in contact with the wick filter element, andwherein the sensor comprises a humidity sensor.
 12. A method ofoperating an apparatus for modifying an ambient air condition, theapparatus including at least one of a heating element and a fan assemblycomprising a motor and a fan blade coupled to a shaft of the motor, andan electronic control circuit electrically coupled to the at leastheating element or motor for providing operating power thereto, theelectronic control circuit including a single control switch and asensor for sensing an ambient air condition, the method comprising thesteps of: actuating the single control switch to turn the apparatus onand off and to select a mode of operation to one of a manual mode and anautomatic mode, wherein actuating the switch in the manual mode selectsan operating power level and wherein actuating the switch in theautomatic mode selects a pre-set threshold ambient air condition value;providing operating power to one of the at least heating element andmotor when in the manual mode; comparing the pre-set threshold ambientair condition to the sensed ambient air condition when in the automaticmode; providing operating power to one of the at least heating elementand motor if the sensed ambient air condition is not substantiallysimilar to the pre-set ambient air condition when the automatic mode;and terminating power to the at least heating element and motor when thepre-set threshold ambient air condition is substantially similar to thesensed ambient air condition when in the automatic mode.
 13. The methodas defined in claim 12, wherein the single control switch is apush-button switch and the step of actuating includes repeatedly pushingthe push-button to progress through the modes of operation and pre-setthreshold ambient air condition values.
 14. The method as defined inclaim 12, wherein the sensor is a thermistor and the apparatus isoperated as a fan.
 15. The method as defined in claim 12, wherein thesensor is a thermistor and the apparatus is a heater.
 16. The method asdefined in claim 12, further including a housing having a means forholding water and a wick filter in contact with water in the housing,and wherein the sensor is a humidity sensor and the apparatus is ahumidifier.
 17. The method as defined in claim 12, wherein the apparatusincludes a housing having a means for holding water and a heatingelement for heating the water to form a mist, and wherein the sensor isa humidity sensor and the apparatus is a humidifier.
 18. An electroniccontrol circuit for operating a device for modifying ambient conditionscomprising: a single control switch for turning the device on and offand selecting a mode of operation, wherein in a manual mode, anoperating power level is selected and wherein in an automatic mode oneof a plurality of pre-set values is selected; a sensor for sensing anambient condition; a comparator for comparing the sensed condition tothe selected pre-set value in the automatic mode; and means forproviding operating power to the device in response to the selected modeof operation and selected setting.
 19. The electronic control circuit asdefined in claim 17, wherein the single control switch is a push-button.20. The electronic control circuit as defined in claim 17, wherein themeans for providing operating power comprises an application-specificintegrated circuit.